Discussions

On my dinner break, I was at a local downtown restaurant. I noticed a pair of shoes,which were tied together, hanging over the branch of the tree. I made a remark to the server, with tongue in cheek, about a new place to hang shoes. She proceeded to tell me that apparently its a way of gangs marking their turf. She said there are shoes hanging in various parts of the city.  
 
I'm so oblivious to things like this........has anyone else heard about this ? If that is the case, why wouldn't police have them removed ? She had said they have been hanging for a couple of months. I certainly wouldn't want to encourage marked areas. Can someone enlighten me to what the "deal" (I love puns....sorry) is on this?